A falling film plate type heat exchanger. The heat exchanger includes a pressure vessel surrounding an encapsulated stack of plates. Each plate has a primary fluid side and a secondary fluid side. The primary fluid will be a refrigerant—such as R-134a. The secondary fluid will typically be water. A film of refrigerant is applied to the primary fluid side of each plate, where it evaporates by absorbing heat from the secondary fluid on the other side of the plate. The invention uses embossed patterns on the plates to direct the flow of the primary and secondary fluids in a desired pattern. Further, the primary fluid side of each plate has a roughened surface treatment to increase the effective surface area and thereby increase the heat transfer rate.